Whether or not you think the functionality would be difficult to implement, you have a better chance of making it happen if you can explain what you want to do with it and why the current interface doesn't serve your needs.

It would be useful for our corpus maintainers. We usually check the newest sentences but the old contributions usually remain unchecked. Moreover, sometimes it's hard to find 1-2 non-native sentences among the latest contributions.

Not that I want to argue about whether we should implement this feature or not, but I’m curious about the way you proofread sentences. I am not a corpus maintainer, so I don’t know what it takes to proofread many many sentences.

As a native speaker of French, I almost only add French sentences, but it doesn’t mean they are free of errors. I regularly get comments about mistakes here and there. It’s mostly more about orthography than naturalness, but still. This makes me think that the amount of trust I’d put in a sentence has more to do with the number and quality of proofreads than the nativeness of the author.

So my point is: shouldn’t sentences be equally checked whether they are from native speakers or not?

> This makes me think that the amount of trust I’d put in a sentence has more to do with the number and quality of proofreads than the nativeness of the author.

It is certainly reasonable, however I think the sentences created by non-native speakers should be checked first. It's not only because they tend to make more mistakes or create more sentences that sound awkward ( as well said in #1907470 )
It's also because non-native sentences that have an OK tag or that are marked as "OK" (i.e. proofread) look more solid and confident so they become more useful.

I agree. It makes sense to focus first on sentences by people who self-identify as having a level lower than the highest possible. They can make not only the mistakes that native speakers might make (such as misspellings), but other ones as well.